Stirling Newberry writes: "Luciano Iess and team have hypothesized that Titan joins Earth, Europa, and Ganymede as ocean worlds. They measure the size of the tidal bulges and find that the moon is likely not solid. Team member Jonathan Lunine points out that Titan's methane atmosphere is not stable, so needs some source, perhaps from outgassing. On earth, water means life, and in the future, ice covered ocean worlds are targets for human colonization, since as the late Arthur C. Clarke observed, water is the most precious substance in the universe to humans."